260 THE VOYAGE OF H.M.S. CHALLENGER. 



the aid of a magnifying glass ; tlie longest rays are about the middle of the tail, where 

 they are about two lines long, free, and extremely delicate ; they disappear at some 

 distance from the end of the tail. The structure of the anal fin is similar, but the rays 

 are on the whole longer and somewhat less delicate. The number of these rays is 

 independent of that of the vertebrae ; two or three may be reckoned to each vertebra. 



The pectoral fins are minute, placed immediately behind,, and a little above, the 

 gill-of)enings ; they have a comparatively broad base and a rounded margin, and are 

 composed of about thirty closely approximate, very thin rays. 



A pair of narrow bluish-white lines commence on the nape and accompanies the 

 dorsal fin, one on each side, until it disappears on the tail. The base of the fin itself 

 runs on a whitish median line which is separated from the lines on the side by a deep 

 black line. Also the anterior part of the anal runs on such a light coloured line, but 

 the lateral lines are very indistinct. 



I cannot see a trace of these lines in our young specimen, which agrees in every 

 respect with the larger one, except in some unimportant points to be mentioned here- 

 after. 



Taking into consideration certain discrepancies in the descriptions given by Mitchill 

 and Harwood, Cuvier as well as Johnson suspected that these authors possibly had 

 distinct species of the same genus before them. However, if no more than due allowance 

 is made for the difliculty in making out the exact proportions and structure of these 

 fragile and more or less distorted and injured objects ; for individual variations, such as 

 the length of the hair-like posterior part of the tail ; for the changes dependent on 

 growth ; and finally for the imperfect observations which in Mitchill's, and still more in 

 Harwood's descriptions are manifest,-^ those discrepancies will be taken at their true 

 value. 



1. Cuvier draws attention to Mitchill's statement that the lower jaw of his fish was 

 toothless. This may have actually been the case, as the teeth are loosely attached to 

 the jaw and readily come ofi" ; or they may have been overlooked by Mitchill, as in 

 our larger specimen such teeth as are still preserved, point inwards, and are hidden 

 under the fold of the skin which runs along the inner margin of the jaw. The 

 mandibulary teeth are decidedly smaller than those of the upper jaw, as is best seen in 

 our smaller example which has them fully preserved. 



2. The relative length of the jaws and of the body, that is, the distance between 

 the snout and vent, seems to undergo a change with growth; at least so it would appear 



' Even in Mr. Johnson's description an observation occurs wliicli, without the type specimen, might have been 

 readily misinterpreted and misused. He says : " What is very remarkable about these (gill-) apertures is that, within 

 the lips of each, the opposite sides are connected by three narrow cutaneous bands, two near the anterior end of the 

 aperture, and one near the posterior end." These three " cutaneous bands " are the third, fourth, and fifth branchial 

 arches which are exposed in the gill-opening. 



